This invention relates to a vehicle lamp with a long curved resin lens.
The lens of a vehicle lamp generally has: a lens body; and a peripheral flange formed around the periphery of the lens body. Usually, the lamp body is so shaped because of a vehicle body design that its vertical width is small, and outside portion (as viewed in the direction of vehicle width) is curved along the vehicle body configuration. This long curved lens is generally a resin lens so that it can be formed with ease.
Even in the case where such a long curved resin lens is employed, the lens body is uniform in thickness as a whole similarly as in the case of an ordinary lens. Hence, the resultant vehicle lamp suffers from the following problems:
The above-described resin lens is generally formed by injection molding. Immediately after the injection molding operation, the behavior of the resin lens is as follows: That is, as shown in FIG. 5(a), in the metal mold 2, the peripheral flange 130 which is large in contact area with the metal mold 2 is firstly solidified, and thereafter the lens body 128 is solidified. During the solidification, the resin contracts. As a result, a compression stress occurs with the lens body 128. The compression strain deformation is considerably large in the longitudinal direction of the lens body 128.
As shown in FIG. 5(b), the flat portion 128A of the lens body 128, which is large in the radius of curvature, substantially causes no problem even if the aforementioned compression strain occurs with the lens body. On the other hand, the curved portion 128B of the lens body 128, which is small in the radius of curvature, causes problems. That is, when the aforementioned compression strain occurs with the lens body, the curved portion 128B is deformed in the direction in which the radius of curvature is increased (or in the direction of the arrow). Because of this deformation, the peripheral flange 130 formed along the periphery of the lens body is deformed downwardly in such a manner that it is moved from its correct position. The peripheral flange 130 is provided for the sealing of the lamp body. If the peripheral flange 130 is deformed in the above-described manner, then its function is not sufficiently performed.
The above-described difficulty accompanies not only with a long curved resin lens which is elongated horizontally but also with a long curved resin lens which is elongated vertically.